scholarly journals PGY Repeats and N-Glycans Govern the Trafficking of Paranodin and Its Selective Association with Contactin and Neurofascin-155

2007 ◽  
Vol 18 (1) ◽  
pp. 229-241 ◽  
Author(s):  
Carine Bonnon ◽  
Christophe Bel ◽  
Laurence Goutebroze ◽  
Bernard Maigret ◽  
Jean-Antoine Girault ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Glial Cells ◽  
Molecular Mechanisms ◽  
Domain Swapping ◽  
Nodes Of Ranvier ◽  
Er Retention ◽  
Processing Signal ◽  
High Mannose

Formation of nodes of Ranvier requires contact of axons with myelinating glial cells, generating specialized axo-glial subdomains. Caspr/paranodin is required for the formation of septate-like junctions at paranodes, whereas the related caspr2 is essential for the organization of juxtaparanodes. The molecular mechanisms underlying the segregation of these related glycoproteins within distinct complexes are poorly understood. Exit of paranodin from the endoplasmic reticulum (ER) is mediated by its interaction with F3/contactin. Using domain swapping with caspr2, we mapped a motif with Pro-Gly-Tyr repeats (PGY) in the ectodomain of paranodin responsible for its ER retention. Deletion of PGY allows cell surface delivery of paranodin bypassing the calnexin-calreticulin quality control. Conversely, insertion of PGY in caspr2 or NrCAM blocks these proteins in the ER. PGY is a novel type of processing signal that compels chaperoning of paranodin by contactin. Contactin associated with paranodin is expressed at the cell surface with high-mannose N-glycans. Using mutant CHO lines altered in the processing of N-linked carbohydrates, we show that the high-mannose glycoform of contactin strongly binds neurofascin-155, its glial partner at paranodes. Thus, the unconventional processing of paranodin and contactin may determine the selective association of axo-glial complexes at paranodes.

scholarly journals The yeast p24 complex regulates GPI-anchored protein transport and quality control by monitoring anchor remodeling

2011 ◽  
Vol 22 (16) ◽  
pp. 2924-2936 ◽  
Author(s):  
Guillaume A. Castillon ◽  
Auxiliadora Aguilera-Romero ◽  
Javier Manzano-Lopez ◽  
Sharon Epstein ◽  
Kentaro Kajiwara ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Intracellular Transport ◽  
Protein Transport ◽  
Eukaryotic Cells ◽  
Secretory Proteins ◽  
Dependent Manner ◽  
Gpi Anchor ◽  
The Status

Glycosylphosphatidylinositol (GPI)-anchored proteins are secretory proteins that are attached to the cell surface of eukaryotic cells by a glycolipid moiety. Once GPI anchoring has occurred in the lumen of the endoplasmic reticulum (ER), the structure of the lipid part on the GPI anchor undergoes a remodeling process prior to ER exit. In this study, we provide evidence suggesting that the yeast p24 complex, through binding specifically to GPI-anchored proteins in an anchor-dependent manner, plays a dual role in their selective trafficking. First, the p24 complex promotes efficient ER exit of remodeled GPI-anchored proteins after concentration by connecting them with the COPII coat and thus facilitates their incorporation into vesicles. Second, it retrieves escaped, unremodeled GPI-anchored proteins from the Golgi to the ER in COPI vesicles. Therefore the p24 complex, by sensing the status of the GPI anchor, regulates GPI-anchored protein intracellular transport and coordinates this with correct anchor remodeling.

scholarly journals Calnexin retains unassembled major histocompatibility complex class I free heavy chains in the endoplasmic reticulum.

1994 ◽  
Vol 180 (1) ◽  
pp. 407-412 ◽  
Author(s):  
S Rajagopalan ◽  
M B Brenner
Keyword(s):  
Endoplasmic Reticulum ◽  
Major Histocompatibility Complex ◽  
Cell Surface ◽  
Mhc Class I ◽  
Cytoplasmic Tail ◽  
Class I ◽  
Major Histocompatibility ◽  
Stable Transfectants ◽  
Histocompatibility Complex ◽  
Er Retention

The assembly of major histocompatibility complex (MHC) class I molecules involves the association of heavy (H) chain with beta 2-microglobulin (beta 2m) and peptide. Unassembled class I H chains do not exit the endoplasmic reticulum (ER) and this is exemplified by the beta 2m-deficient human melanoma FO-1 where free class I H chains are unable to complete assembly. In pulse chase experiments involving FO-1 cells, unassembled free class I H chains were shown to be stably associated with calnexin (IP90/p88), a 90-kD integral membrane molecular chaperone of the ER. To establish a role for calnexin in mediating this retention, we transfected FO-1 cells with a cytoplasmic tail deletion mutant of calnexin. Since the cytoplasmic tail contains the ER retention motif, these mutant calnexin molecules leave the ER and progress to the cell surface. In these stable transfectants of FO-1, free class I H chains also exited the ER and trafficked to the cell surface with calnexin, thus establishing a role for calnexin in the quality control of MHC class I assembly through mediating the ER retention of incompletely assembled class I H chains.

scholarly journals Syntaxin 8 and the Endoplasmic Reticulum Processing of ΔF508-CFTR

2018 ◽  
Vol 51 (3) ◽  
pp. 1489-1499 ◽  
Author(s):  
Inna Sabirzhanova ◽  
Clément Boinot ◽  
William B. Guggino ◽  
Liudmila Cebotaru
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Common Mutation ◽  
Early Endosomes ◽  
Δf508 Cftr ◽  
Quality Control Mechanism ◽  
Cf Transmembrane Conductance Regulator

Background/Aims: Cystic fibrosis (CF) is a lethal recessive disorder caused by mutations in the CF transmembrane conductance regulator (CFTR). ΔF508, the most common mutation, is a misfolded protein that is retained in the endoplasmic reticulum and degraded, precluding delivery to the cell surface [<xref ref-type="bibr" rid="ref1">1</xref>]. Methods: Here we use a combination of western blotting, immunoprecipitation, and short circuit current techniques combined with confocal microscopy to address whether the SNARE attachment protein, STX8 plays a role in ΔF508’s processing and movement out of the ER. Results: Although the SNARE protein STX8 is thought to be functionally related and primarily localized to early endosomes, we show that silencing of STX8, particularly in the presence of the Vertex corrector molecule C18, rescues ΔF508-CFTR, allowing it to reach the cell surface and increasing CFTR-dependent chloride currents by approximately 2.5-fold over control values. STX8 silencing reduced the binding of quality control protein, Hsp 27, a protein that targets ΔF508-CFTR for sumoylation and subsequent degradation, to ΔF508-CFTR. STX8 silencing increased the levels of Hsp 60 a protein involving in early events in protein folding. Conclusion: STX8 knockdown creates an environment favorable for mature ΔF508 to reach the cell surface. The data also suggest that when present at normal levels, STX8 functions as part of the cell’s quality control mechanism.

scholarly journals SAT-LB137 Rescue of Misfolded G-Protein Coupled Estrogen Receptor, GPER, from the Endoplasmic Reticulum via Natural and Synthetic Estrogens

2020 ◽  
Vol 4 (Supplement_1) ◽  
Author(s):  
Milad Rouhimoghadam ◽  
Jing Dong ◽  
Peter Thomas ◽  
Edward Joseph Filardo
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Cell Surface ◽  
G Protein ◽  
Surface Expression ◽  
Membrane Expression ◽  
Plasma Membrane Expression ◽  
17Β Estradiol ◽  
G Protein Coupled

Abstract GPER bears structural and functional characteristics shared by members of the G-protein coupled receptor (GPCR) superfamily, the largest class of cell surface receptors, with more than 800 members encoded in the human genome. GPER is localized predominately in intracellular membranes, in many but not all cell types, and its surface expression is modulated by steroid hormones and during tissue homeostasis. An intracellular staining pattern is not unique among GPCRs, which deploy a diverse array of posttranslational regulatory mechanisms to determine cell surface expression, effectively regulating cognate ligand binding and activity. Here, we show nascent GPER undergoes strict quality control via endoplasmic reticulum associated degradation (ERAD) requiring direct poly-ubiquitinylation of GPER and valosin-containing protein VCP/p97-mediated segregation of misfolded proteins from the ER membrane to the cytoplasm for delivery to the 26S proteasome. Specifically, we find that inhibition of p97 using the pharmacological compound, CB-5083, or by doxycycline-inducible p97 shRNA results in the accumulation of immature glycosylated GPER in the ER. Inhibition of proteasome function facilitates anterograde trafficking with the transport of nonfunctional GPER to the plasma membrane as indicated by no increase in specific estrogen binding using 3H-17β-estradiol in a radioreceptor assay. The forward trafficking of misfolded GPER requires transit through the Golgi as treatment with brefeldin A (BFA) prevents GPER plasma membrane expression. Substitution of all three lysines (K333, K342, and K357) encoded in the cytoplasmic tail of GPER with arginines blunts its polyubiquitinylation and allows GPER to evade degradation by quality control but does not result in increased plasma membrane expression suggesting that additional structural motifs encoded within GPER control its anterograde trafficking. In contrast, functional GPER is recovered at the plasma membrane of human SKBR3 breast cancer cells treated with either 17β-estradiol or the GPER selective antagonist, G15, in the presence of cycloheximide resulting in increased surface GPER. Thus, our findings suggest that estrogens, both natural and synthetic, can function as pharmacochaperones capable of promoting the correct folding of GPER and enhanced expression of functional GPER at the plasma membrane.

scholarly journals Molecular mechanisms that regulate export of the planar cell-polarity protein Frizzled-6 out of the endoplasmic reticulum

2020 ◽  
Vol 295 (27) ◽  
pp. 8972-8987
Author(s):  
Xiao Tang ◽  
Lina Zhang ◽  
Tianji Ma ◽  
Mo Wang ◽  
Baiying Li ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Cell Polarity ◽  
Planar Cell Polarity ◽  
Molecular Mechanisms ◽  
Protein Transport ◽  
Direct Interaction ◽  
Intracellular Loop ◽  
Transport Pathway ◽  
Secretory Transport

Planar cell polarity (PCP) is a process during which cells are polarized along the plane of the epithelium and is regulated by several transmembrane signaling proteins. After their synthesis, these PCP proteins are delivered along the secretory transport pathway to the plasma membrane, where they perform their physiological functions. However, the molecular mechanisms that regulate PCP protein transport remain largely unclear. Here, we found that the delivery of a PCP protein, Frizzled-6, to the cell surface is regulated by two conserved polybasic motifs: one located in its first intracellular loop and the other in its C-terminal cytosolic domain. We observed that the polybasic motif of Frizzled is also important for its surface localization in the Drosophila wing. Results from a mechanistic analysis indicated that Frizzled-6 packaging into vesicles at the endoplasmic reticulum (ER) is regulated by a direct interaction between the polybasic motif and the Glu-62 and Glu-63 residues on the secretion-associated Ras-related GTPase 1A (SAR1A) subunit of coat protein complex II (COPII). Moreover, we found that newly synthesized Frizzled-6 is associated with another PCP protein, cadherin EGF LAG seven-pass G-type receptor 1 (CELSR1), in the secretory transport pathway, and that this association regulates their surface delivery. Our results reveal insights into the molecular machinery that regulates the ER export of Frizzled-6. They also suggest that the association of CELSR1 with Frizzled-6 is important, enabling efficient Frizzled-6 delivery to the cell surface, providing a quality control mechanism that ensures the appropriate stoichiometry of these two PCP proteins at cell boundaries.

scholarly journals Endoplasmic Reticulum Quality Control of Unassembled Iron Transporter Depends on Rer1p-mediated Retrieval from the Golgi

2004 ◽  
Vol 15 (3) ◽  
pp. 1417-1424 ◽  
Author(s):  
Miyuki Sato ◽  
Ken Sato ◽  
Akihiko Nakano
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Model System ◽  
Er Quality Control ◽  
Iron Transporter ◽  
Er Retention ◽  
Endoplasmic Reticulum Quality Control ◽  
Sorting Receptor

Endoplasmic reticulum (ER) quality control is a conserved process by which misfolded or unassembled proteins are selectively retained in the endoplasmic reticulum (ER). Failure in oligomerization of multisubunit membrane proteins is one of the events that triggers ER quality control. The transmembrane domains (TMDs) of unassembled subunits are determinants of ER retention in many cases, although the mechanism of the TMD-mediated sorting of unassembled subunits remains elusive. We studied a yeast iron transporter complex on the cell surface as a new model system for ER quality control. When Fet3p, a transmembrane subunit, is not assembled with the other membrane subunit, Ftr1p, unassembled Fet3p is exclusively localized to the ER at steady state. The TMD of Fet3p contains a determinant for this process. However, pulse-chase analysis and in vitro budding assays indicate that unassembled Fet3p rapidly escapes from the ER. Furthermore, Rer1p, a retrieval receptor for ER-resident membrane proteins in the Golgi, is responsible for the TMD-dependent ER retrieval of unassembled Fet3p. These findings provide clear evidence that the ER quality control of unassembled membrane proteins can be achieved by retrieval from the Golgi and that Rer1p serves as a specific sorting receptor in this process.

Endoplasmic reticulum quality control and dysmyelination

2011 ◽  
Vol 2 (4) ◽  
pp. 261-274 ◽  
Author(s):  
Allison Kraus ◽  
Marek Michalak
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Molecular Mechanisms ◽  
Review Paper ◽  
Cholesterol Biosynthesis ◽  
Charcot Marie Tooth ◽  
Myelin Sheaths ◽  
Conduction Velocities ◽  
Endoplasmic Reticulum Quality Control

AbstractDysmyelination contributes to several human diseases including multiple sclerosis, Charcot-Marie-Tooth, leukodystrophies, and schizophrenia and can result in serious neurological disability. Properly formed, compacted myelin sheaths are required for appropriate nerve conduction velocities and the health and survival of neurons. Many different molecular mechanisms contribute to dysmyelination and many of these mechanisms originate at the level of the endoplasmic reticulum. The endoplasmic reticulum is a critical organelle for myelin biosynthesis and maintenance as the site of myelin protein folding quality control, Ca2+ homeostasis, cholesterol biosynthesis, and modulation of cellular stress. This review paper highlights the role of the endoplasmic reticulum and its resident molecules as an upstream and dynamic contributor to myelin and myelin pathologies.

scholarly journals How Is the Fidelity of Proteins Ensured in Terms of Both Quality and Quantity at the Endoplasmic Reticulum? Mechanistic Insights into E3 Ubiquitin Ligases

2021 ◽  
Vol 22 (4) ◽  
pp. 2078
Author(s):  
Ji An Kang ◽  
Young Joo Jeon
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Molecular Mechanisms ◽  
Protein Quality ◽  
Protein Quality Control ◽  
Ubiquitin Ligases ◽  
Ubiquitin Proteasome System ◽  
Misfolded Proteins ◽  
E3 Ubiquitin Ligases ◽  
Quantity Control

The endoplasmic reticulum (ER) is an interconnected organelle that plays fundamental roles in the biosynthesis, folding, stabilization, maturation, and trafficking of secretory and transmembrane proteins. It is the largest organelle and critically modulates nearly all aspects of life. Therefore, in the endoplasmic reticulum, an enormous investment of resources, including chaperones and protein folding facilitators, is dedicated to adequate protein maturation and delivery to final destinations. Unfortunately, the folding and assembly of proteins can be quite error-prone, which leads to the generation of misfolded proteins. Notably, protein homeostasis, referred to as proteostasis, is constantly exposed to danger by flows of misfolded proteins and subsequent protein aggregates. To maintain proteostasis, the ER triages and eliminates terminally misfolded proteins by delivering substrates to the ubiquitin–proteasome system (UPS) or to the lysosome, which is termed ER-associated degradation (ERAD) or ER-phagy, respectively. ERAD not only eliminates misfolded or unassembled proteins via protein quality control but also fine-tunes correctly folded proteins via protein quantity control. Intriguingly, the diversity and distinctive nature of E3 ubiquitin ligases determine efficiency, complexity, and specificity of ubiquitination during ERAD. ER-phagy utilizes the core autophagy machinery and eliminates ERAD-resistant misfolded proteins. Here, we conceptually outline not only ubiquitination machinery but also catalytic mechanisms of E3 ubiquitin ligases. Further, we discuss the mechanistic insights into E3 ubiquitin ligases involved in the two guardian pathways in the ER, ERAD and ER-phagy. Finally, we provide the molecular mechanisms by which ERAD and ER-phagy conduct not only protein quality control but also protein quantity control to ensure proteostasis and subsequent organismal homeostasis.

scholarly journals N-Glycan–dependent protein folding and endoplasmic reticulum retention regulate GPI-anchor processing

2017 ◽  
Vol 217 (2) ◽  
pp. 585-599 ◽  
Author(s):  
Yi-Shi Liu ◽  
Xin-Yu Guo ◽  
Tetsuya Hirata ◽  
Yao Rong ◽  
Daisuke Motooka ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Folding ◽  
Cell Surface ◽  
Er Stress ◽  
Posttranslational Modification ◽  
Acyl Chain ◽  
Genetic Screens ◽  
Gpi Anchor ◽  
Er Retention ◽  
Dependent Protein

Glycosylphosphatidylinositol (GPI) anchoring of proteins is a conserved posttranslational modification in the endoplasmic reticulum (ER). Soon after GPI is attached, an acyl chain on the GPI inositol is removed by post-GPI attachment to proteins 1 (PGAP1), a GPI-inositol deacylase. This is crucial for switching GPI-anchored proteins (GPI-APs) from protein folding to transport states. We performed haploid genetic screens to identify factors regulating GPI-inositol deacylation, identifying seven genes. In particular, calnexin cycle impairment caused inefficient GPI-inositol deacylation. Calnexin was specifically associated with GPI-APs, dependent on N-glycan and GPI moieties, and assisted efficient GPI-inositol deacylation by PGAP1. Under chronic ER stress caused by misfolded GPI-APs, inositol-acylated GPI-APs were exposed on the cell surface. These results indicated that N-glycans participate in quality control and temporal ER retention of GPI-APs, ensuring their correct folding and GPI processing before exiting from the ER. Once the system is disrupted by ER stress, unprocessed GPI-APs become exposed on the cell surface.

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